JP2007250416A - Nonaqueous electrolyte secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high output by using polyimide as binder resin, enhancing binding between a negative electrode core and a negative electrode mix layer even if rolled copper foil is used as the negative electrode core, preventing peeling off of the negative electrode mix layer from the negative electrode core, and hardly forming a resistive element on the interface between the negative electrode core and the negative electrode mix layer. <P>SOLUTION: The nonaqueous electrolyte secondary battery 10 is equipped with a positive plate 11 in which the positive electrode mix layer 11b containing a lithium transition metal composite oxide capable of absorbing/releasing lithium as a positive active material is formed on the positive electrode core 11a; a negative plate 12 in which the negative electrode mix layer 12b containing carbon capable of absorbing/releasing lithium as a negative active material is formed on the negative electrode core 12a; and a nonaqueous electrolyte containing a lithium salt. Polyimide is contained in the negative electrode mix layer 12b as a binder, and rolled copper foil applied with no corrosion prevention treatment is used as the negative electrode core 12b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a positive electrode plate on which a positive electrode mixture layer containing a lithium transition metal composite oxide capable of occluding and releasing lithium as a positive electrode active material and carbon capable of occluding and releasing lithium as a negative electrode active material. The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode plate having a negative electrode mixture layer formed thereon and a non-aqueous electrolyte to which a lithium salt is added, and a method for manufacturing the same.

In recent years, as a battery used in portable electronic / communication equipment such as a small video camera, a mobile phone, and a laptop computer, a carbon material that can occlude / release lithium ions is used as a negative electrode active material, lithium cobalt oxide (LiCoO ₂ ), Non-aqueous electrolyte secondary batteries using lithium-containing transition metal oxides such as lithium manganate (LiMn ₂ O ₄ ) and lithium nickelate (LiNiO ₂ ) as a positive electrode active material are small, light, high in voltage, and high in capacity. It has come into practical use as a chargeable / dischargeable battery.

  Since this type of non-aqueous electrolyte secondary battery has a relatively large current consumption and can withstand heavy loads, the strip-like positive electrode plate and the strip-like negative electrode plate are wound in the length direction via a separator. It is effective to use a spiral electrode group formed by turning. In this spiral electrode group, it is desirable to make the electrode plate thin in order to increase the electrode plate area and fill the active material layer (mixture layer) as much as possible in the limited space. Therefore, conventionally, a paste-like mixture in which a granular active material is dispersed in a binder is applied on an electrode plate core and dried to form an active material layer (mixture layer), thereby forming a strip-like electrode. The board was manufactured.

  According to this method, the thickness of the active material layer (mixture layer) in the strip-shaped electrode plate can be set to about several μm to several hundred μm. However, in the manufacturing method in which coating and drying are performed as described above, there is a problem that the processing cost is high, and the binder resin used is limited to those that dissolve or disperse in an organic solvent or water. . Therefore, a conductive film such as a metal foil is used for the electrode plate core of this type of battery, and a negative electrode mixture in which a granular carbonaceous material and a binder resin are kneaded is extruded and laminated on the conductive film. Patent Document 1 has proposed a method for producing a negative electrode having a step of forming an active material layer (mixture layer) of an active material.

In the method for producing a negative electrode proposed in Patent Document 1, the binder resin is at least one selected from polyimide, polyamide, polyamideimide, fluororesin, diene rubber, acrylic resin, polyolefin, polyester, polyurethane, and polyarylate. A negative electrode active material layer (negative electrode mixture layer) is formed by extruding and laminating a mixture in which a granular carbonaceous material and a binder resin are kneaded onto a conductive film made of copper foil or the like. I have to.
JP-A-10-302798

  However, as proposed in Patent Document 1 described above, a negative electrode mixture containing a binder resin such as polyimide is extruded and laminated on a conductive film made of copper foil to form a negative electrode active material layer (negative electrode mixture layer). When the electrode is formed, the binding force between the conductive film made of copper foil and the negative electrode active material layer (negative electrode mixture layer) is not sufficient, and the negative electrode active material layer (negative electrode mixture layer) is peeled off during negative electrode rolling. There was a problem of inferiority.

  This is because a rolled copper foil is used as the copper foil used as the conductive film, and this type of rolled copper foil is usually rust-proofed with benzotriazole or the like. By the way, the binding force between a rolled copper foil subjected to rust prevention treatment and a binder resin such as polyimide is weak, and a mixture layer containing a binder resin such as polyimide is formed on the rolled copper foil subjected to rust prevention treatment. However, there was a problem that the mixture layer was peeled off from the rolled copper foil during rolling. This is because the rust-proofing layer is formed on the surface of the rolled copper foil, so that the adhesion between the rust-proofing layer and the negative electrode mixture layer becomes insufficient, and the rolled copper foil and the negative electrode mixture layer This is because the adhesion is reduced.

  Therefore, the present invention has been made based on such problems, and while using polyimide as a binder resin and using rolled copper foil as a core of a negative electrode mixture, a negative electrode core and a negative electrode mixture Improving the binding force with the layer, providing a negative electrode in which the negative electrode mixture layer does not peel from the negative electrode core, and making it difficult for a resistor to be formed at the interface between the negative electrode core and the negative electrode mixture layer, An object of the present invention is to provide a high-power nonaqueous electrolyte secondary battery.

  The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode plate in which a positive electrode mixture layer containing a lithium transition metal composite oxide capable of occluding and releasing lithium as a positive electrode active material is formed on a positive electrode core, and occlusion of lithium -It has the negative electrode plate in which the negative mix layer containing carbon which can be discharge | released as a negative electrode active material was formed in the negative electrode core body, and the non-aqueous electrolyte to which lithium salt was added. The negative electrode mixture layer contains polyimide as a binder, and the negative electrode core is a rolled copper foil that has not been subjected to rust prevention treatment.

  Here, when an electrolytic copper foil that has undergone rust prevention treatment (for example, chromate treatment) or a rolled copper foil that has undergone rust prevention treatment (for example, benzotriazole treatment) is used for the negative electrode core, a treatment layer of a rust prevention agent is formed on the surface. Will be. For this reason, the adhesion between the negative electrode core and the negative electrode mixture layer becomes insufficient, and the peel strength decreases. On the other hand, when a rolled copper foil that has not been rust-proofed is used for the negative electrode core, there is no rust-proofing layer on the surface, so the adhesion between the negative electrode core and the negative electrode mixture layer is improved. As a result, the peel strength is improved. In addition, even if the negative electrode core is not subjected to rust prevention treatment, if the adhesion between the negative electrode core and the negative electrode mixture layer is sufficient, the negative electrode core is prevented from coming into direct contact with the electrolytic solution. The negative electrode core is not corroded.

  When the peel strength is improved and the adhesion between the negative electrode core and the negative electrode mixture layer is improved, the negative electrode core is prevented from coming into direct contact with the electrolyte solution. A film formed by contact with the electrolytic solution is not formed at the interface with the negative electrode mixture layer, and the resistor is hardly formed. As described above, since the adhesion between the negative electrode core and the negative electrode mixture layer is improved, the negative electrode mixture layer is hardly peeled off from the negative electrode core, so that a negative electrode plate having excellent productivity can be produced. Become. Moreover, since it becomes difficult for a resistor to be formed at the interface between the negative electrode core and the negative electrode mixture layer, a high-power battery can be produced.

  In this case, it is generally known that polyimide is inferior in binding force before heat treatment of the negative electrode plate. On the other hand, since the polyimide formed by heat-treating polyamic acid has excellent binding power, it is desirable that the polyimide as the binder is formed by heat-treating polyamic acid.

And in order to manufacture the battery containing the polyimide as a binder in such a negative electrode mixture layer, a rolled copper foil not subjected to rust prevention treatment is used as a negative electrode core. A negative electrode forming step of forming a negative electrode mixture layer by applying a negative electrode mixture slurry prepared by adding polyamic acid to the negative electrode active material, and a heat treatment of the negative electrode in which the negative electrode mixture layer is formed on the negative electrode core And a heat treatment step for changing the polyamic acid added to the negative electrode mixture to polyimide.
In addition, as for the heat processing temperature in a heat processing process, it is desirable that it is 300 to 400 degreeC. This is because when the heat treatment temperature is less than 300 ° C., the polyamic acid cannot be sufficiently changed to polyimide, and when it exceeds 400 ° C., the softening of the copper foil proceeds.

  In the present invention, the negative electrode core is a rolled copper foil that has not been subjected to rust prevention treatment, and since the negative electrode mixture layer contains polyimide as a binder, the negative electrode core and the negative electrode mixture It becomes possible to produce a negative electrode having improved productivity due to improved adhesion to the layer. Moreover, since it becomes difficult for a resistor to be formed at the interface between the negative electrode core and the negative electrode mixture layer, it is possible to provide a high-power nonaqueous electrolyte secondary battery.

  Next, an embodiment of the present invention will be described below. However, the present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that does not change the object of the present invention. is there. In addition, FIG. 1 is sectional drawing which shows typically the nonaqueous electrolyte secondary battery of this invention.

1. The positive electrode plate Li ₂ CO ₃ and (Ni _0.4 Co _0.3 Mn _0.3 ) ₃ O ₄ have a molar ratio of Li to (Ni _0.4 Co _0.3 Mn _0.3 ) of 1: 1 (Li: (Ni _0.4 Co _0.3 Mn _0.3 ). = 1: 1). Subsequently, this mixture was fired at 900 ° C. for 20 hours in an air atmosphere to obtain a lithium transition metal oxide represented by LiNi _0.4 Co _0.3 Mn _0.3 O ₂ having an average particle size of 12.1 μm, and a positive electrode active material It was.

  The positive electrode active material obtained as described above, the carbon powder as the conductive agent, and the polyvinylidene fluoride (PVdF) as the binder were N— in a mass ratio of 92: 5: 3. It was added to methyl-2-pyrrolidone (NMP) and kneaded to prepare a positive electrode slurry. The produced positive electrode slurry was applied on an aluminum foil as the positive electrode core 11a and then dried to form the positive electrode active material layer 11b. Then, it rolled until it became a predetermined packing density using the rolling roll, and after cut | disconnecting to the predetermined dimension, the positive electrode current collection tab 11c was attached and the positive electrode plate 11 was produced.

2. Negative electrode plate (1) Negative electrode core 1
After preparing a rolled copper foil having a thickness of 9 μm (non-rust-proof treated rolled copper foil), it was cut into a predetermined size to form a negative electrode core 12a, which was defined as a core α. Also, after preparing a rolled copper foil (rolled copper foil with benzotriazole treatment) having a thickness of 9 μm and rust-prevented with a benzotriazole treatment solution, it is cut into a predetermined dimension to form a negative electrode core 12a, which is the core β. Further, after preparing an electrolytic copper foil (chromium-treated electrolytic copper foil) having a thickness of 9 μm and anti-rust treated with a chromate treatment solution, it is cut into a predetermined dimension to form a negative electrode core 12a, which is a core δ. did.

(2) Negative electrode plate Next, an aqueous solution in which artificial graphite as a negative electrode active material was dissolved and a polyamic acid solution as a binder were kneaded to prepare a negative electrode slurry. In this case, these were added so that the mass ratio of the solid content of the negative electrode active material: binder was 97: 3. Next, the prepared negative electrode slurry was applied onto the negative electrode core 12a (non-rust-proof treated rolled copper foil α, benzotriazole-treated rolled copper foil β, chromate-treated electrolytic copper foil δ) produced as described above. . Thereafter, the negative electrode active material layer 12b was formed by drying.

  Then, after rolling to a predetermined filling density using a rolling roller, a heat treatment was performed at a temperature of 350 ° C. for 120 minutes in an inert atmosphere. This heat treatment changes the polyamic acid to polyimide. Next, after cutting to a predetermined size, a negative electrode current collecting tab 12c was attached to produce a negative electrode plate 12 (a, b, c). The non-rust-proof treated rolled copper foil α is used as the core 12a as the negative electrode plate a, the benzotriazole-treated rolled copper foil β is used as the core 12a as the negative plate b, and the chromate-treated electrolytic A negative electrode plate c was prepared using the copper foil δ as the core 12a.

3. Measurement of peel strength Next, the negative plates a, b, c after rolling and before heat treatment and the negative plates a, b, c after rolling and heat treatment were used to determine the peel strength of these negative plates a, b, c. The results shown in Table 1 below were obtained. The peel strength was determined as follows. First, the negative electrode active material layer 12b is formed on the negative electrode core 12a, and the negative electrode plate 12 (a, b, c) after the rolling treatment (before heat treatment and after heat treatment) is fixed. Next, after sticking a certain area of the adhesive tape on the surface of the negative electrode active material layer 12b, the force to pull up the adhesive tape was gradually increased, and the force applied when peeling occurred was determined. And peel strength (kg / cm < ² >) was computed from the calculated | required force and the area of an adhesive tape.

  As is clear from the results of Table 1 above, in the negative electrode plate c using the chromate-treated electrolytic copper foil δ as the core body 12a, the peel strength is small in both the peel strength after rolling and the peel strength after rolling and heat treatment. It became clear that it was not practical. Further, in the negative electrode plate b using the benzotriazole-treated (rust-proofed) rolled copper foil β as the core body 12a, both the peel strength after rolling and the peel strength after rolling and heat treatment are separated from the negative plate c. It can be seen that although the strength is large, it is difficult to say that it has sufficient peel strength. On the other hand, in the negative electrode plate a using the non-rust-proof treated rolled copper foil α as the core body 12a, it has excellent peel strength in both the peel strength after rolling and the peel strength after rolling and heat treatment. I understand.

  This is because the negative electrode core 12a made of the chromate-treated electrolytic copper foil δ has a chromate treatment layer formed on the surface thereof, so that the adhesion between the negative electrode core 12a and the negative electrode mixture layer 12b becomes insufficient. It is considered that the peel strength after rolling and the peel strength after rolling and heat treatment were lowered. In addition, in the negative electrode core 12a made of the rolled copper foil β having been treated with benzotriazole, since the benzotriazole-treated layer is formed on the surface thereof, the adhesion between the negative electrode core 12a and the negative electrode mixture layer 12b is insufficient. Thus, it is considered that the peel strength after rolling and the peel strength after rolling and heat treatment were lowered. On the other hand, in the negative electrode core 12a made of the non-rust-proof treated rolled copper foil α, since the rust-proof layer does not exist on the surface, the adhesion between the negative electrode core 12a and the negative electrode mixture layer 12b is improved. Thus, it is considered that the peel strength after rolling and the peel strength after rolling / heat treatment were improved.

4). Non-aqueous electrolyte secondary battery Next, each positive electrode plate 11 manufactured as described above and the negative electrode plate 12 (a, b) manufactured as described above were used, respectively, and a polyethylene microporous film was interposed between them. Then, the separators 13 were stacked, and then wound in a spiral shape to form a spiral electrode group. In addition, in the negative electrode plate c, the spiral electrode group could not be produced using the negative electrode plate c due to insufficient strength.

  Next, these spiral electrode groups are inserted into cylindrical metal outer cans 14 each having a drawing portion 14a formed by drawing the upper outer periphery, and then a negative electrode current collecting tab 12c extending from the negative electrode plate 12 is provided. It welded to the inner bottom face of the metal outer can 14. On the other hand, a positive electrode current collecting tab 11 c extending from the positive electrode plate 11 was welded to the bottom surface of the positive electrode lid 15 b of the sealing body 15, and a ring-shaped insulating gasket 16 was disposed on the outer periphery of the sealing body 15. A cap-like positive electrode terminal 15a is disposed on the upper portion of the positive electrode lid 15b, and a valve for sealing an exhaust hole 15c formed at the center of the positive electrode lid 15b in the cap-like positive electrode terminal 15a. A valve body including a plate 15d and a spring 15e that presses the plate 15d is disposed.

Subsequently, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) is used as a solute with respect to a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3: 7. A nonaqueous electrolytic solution dissolved at a rate of 1 liter was poured into the metal outer can 14. Thereafter, after the sealing body 15 having the ring-shaped insulating gasket 16 disposed on the outer peripheral portion is disposed on the narrowed portion 14a formed on the upper outer periphery of the metal outer can 14, the upper end of the metal outer can 14 is disposed. The portion 14b was caulked and sealed to the sealing body 15 side. Thereby, the nonaqueous electrolyte secondary battery 10 (A, B) having a design capacity of 4.6 Ah was produced. A battery using the negative electrode plate a was designated as battery A, and a battery using the negative electrode plate b was designated as battery B.

5). Battery Characteristic Test Next, the non-aqueous electrolyte secondary batteries A and B produced as described above were charged to 4.1 V with a charging current of 1 It at room temperature of 25 ° C., respectively, and the voltage was further increased to 4.1 V. The charge current was decreased while maintaining, and the battery was charged until the charge current became 1/20 It, then discharged to 3.0 V with a discharge current of 1/3 It, and the discharge capacity was measured. In addition, the batteries A and B were charged at a current of 1/3 It, 1 It, 3 It, and 5 It, respectively, at a room temperature of 25 ° C. with a charging current of 1 It until the depth of charge (SOC) reached 50%. Charging and discharging for 10 seconds, measuring each battery voltage, plotting each current value and battery voltage to determine the IV characteristics at the time of charging and discharging, and from the slope of the obtained straight line and When the IV resistance (mΩ) at the time of discharge was obtained, the results shown in Table 2 were obtained.

  As is apparent from the results in Table 2, in the battery B including the negative electrode plate b using the benzotriazole-treated (rust-proofed) rolled copper foil β as the core body 12a, the IV resistance during charging was 3. It can be seen that the IV resistance during discharge is 3.6 mΩ at 1 mΩ. On the other hand, in the battery A provided with the negative electrode plate a using the non-rust-proof treated rolled copper foil α as the core body 12a, the IV resistance during charging was 2.9 mΩ, and the IV resistance during discharging was 3.4 mΩ. It turns out that it is reducing rather than B.

  This is because, in the negative electrode of the battery A, the non-rust-proof treated rolled copper foil α is used as the negative electrode core 12a. Therefore, both the peel strength after rolling and the peel strength after rolling and heat treatment are improved. This is probably because the core 12a is prevented from coming into direct contact with the electrolytic solution due to the improved adhesion with the mixture layer 12b. As described above, when the core body 12a is prevented from coming into direct contact with the electrolytic solution, a film generated by contact with the electrolytic solution is not formed at the interface between the core body 12a and the negative electrode mixture layer 12b. This is thought to be because the resistance body is difficult to be formed.

  As described above, in the present invention, the negative electrode core is a rolled copper foil that has not been subjected to rust prevention treatment, and the negative electrode mixture layer contains polyimide as a binder. The adhesion between the body and the negative electrode mixture layer is improved, and a negative electrode with excellent productivity can be produced. Moreover, since it becomes difficult for a resistor to be formed at the interface between the negative electrode core and the negative electrode mixture layer, it is possible to provide a high-power nonaqueous electrolyte secondary battery.

In the above-described embodiment, the example in which the heat treatment after rolling is performed in an inert atmosphere at a temperature of 350 ° C. for 120 minutes has been described. However, the heat treatment time is desirably set to 10 minutes or more. This is because if it is less than 10 minutes, the polyamic acid cannot be sufficiently changed to polyimide. In the above-described embodiment, an example in which LiNi _0.4 Co _0.3 Mn _0.3 O ₂ is used as a lithium transition metal oxide has been described. However, lithium transition metal oxides other than LiNi _0.4 Co _0.3 Mn _0.3 O ₂ may be used. However, if it is a lithium transition metal oxide capable of occluding and releasing lithium, almost the same result as described above can be expected.

It is sectional drawing which shows typically the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Non-aqueous electrolyte secondary battery, 11 ... Positive electrode plate, 11a ... Positive electrode core, 11b ... Positive electrode mixture layer, 11c ... Positive electrode current collection tab, 12 ... Negative electrode plate, 12a ... Negative electrode core, 12b ... Negative electrode mixture Layer, 12c ... negative electrode current collecting tab, 13 ... separator, 14 ... metal outer can, 14a ... throttle part, 15 ... sealing body, 15a ... positive electrode terminal, 15b ... positive electrode lid, 15c ... exhaust hole 15d ... valve plate, 15e ... Spring, 16 ... Insulating gasket

Claims (4)

A positive electrode plate having a positive electrode mixture layer containing a lithium transition metal composite oxide capable of occluding and releasing lithium as a positive electrode active material, and carbon capable of occluding and releasing lithium as a negative electrode active material A non-aqueous electrolyte secondary battery comprising a negative electrode plate having a negative electrode mixture layer formed on a negative electrode core and a non-aqueous electrolyte to which a lithium salt is added,
A non-aqueous electrolyte secondary battery characterized in that polyimide as a binder is contained in the negative electrode mixture layer, and the negative electrode core is a rolled copper foil not subjected to rust prevention treatment.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the polyimide as the binder is formed by heat-treating polyamic acid contained in the negative electrode mixture layer. A positive electrode plate having a positive electrode mixture layer containing a lithium transition metal composite oxide capable of occluding and releasing lithium as a positive electrode active material, and carbon capable of occluding and releasing lithium as a negative electrode active material A negative electrode plate including a negative electrode mixture layer formed on a negative electrode core, and a non-aqueous electrolyte secondary battery manufacturing method including a non-aqueous electrolyte to which a lithium salt is added,
A rolled copper foil that has not been subjected to rust prevention treatment is used as the negative electrode core, and a negative electrode mixture slurry prepared by adding polyamic acid to the negative electrode active material is applied to the negative electrode core. A negative electrode mixture layer forming step of forming a layer;
A non-aqueous electrolyte comprising: a heat treatment step of heat-treating the negative electrode plate having a negative electrode mixture layer formed on the negative electrode core to change the polyamic acid added to the negative electrode mixture to polyimide. A method for manufacturing a secondary battery. The method for manufacturing a nonaqueous electrolyte secondary battery according to claim 3, wherein a heat treatment temperature in the heat treatment step is 300 ° C. to 400 ° C. 5.

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